Phew...
No tech refs available in my present location, Bob, but am fairly confident that the IRS wind deteriorates in accuracy as a function of how long it is since you aligned the IRUs. [For the uninitiated, this is nothing to do with position updating; the only time you can re-align an IRS is when the aircraft is stationary.]
This can be illustrated by the growing disparity between the instant W/Vs provided by the different FMCs, which typically use differing IRUs for W/V.
IRS PPOS error is proportional, roughly speaking, to time, and - in pre-laser INS days, used to be recorded in the Tech Log for each INS on arrival at destination (retrofitted B707s, et al). It can be expressed in knots.
For what it's worth, I'd never base a decision to land or G/A on the basis of an IRS W/V readout at 100ft or 50 ft - unless, of course, the decision was to go-around. In addition to the above, there can be considerable shear between 100ft and the surface. Airfields with local W/V effects near a Rwy threshold should have nearby anemometers, although in the real world...
Thanks for the opportunity to avoid contributing to a messy discussion involving speculative justice on Ryanair pilots.